Conventionally, when driving a screw, devices such as one disclosed in the Japanese Utility Model Publication No. Sho 46-35987, wherein air attraction is employed to attract a screw to the tip of a driver bit, have been utilized. Also, for example, the Publication of Unexamined Japanese Utility Model Application No. Sho 57-202669 discloses a device, wherein magnetic force is employed to attract a screw to the tip of a driver bit by magnetizing the driver bit using one or more permanent magnets.
In the case where air attraction is employed, however, it is necessary to fit a device adapted for air attraction around a driver bit. Therefore, when driving a screw into an object having a counterbore, the driver bit with such a device cannot be used because the outside diameter thereof is relatively large. Moreover, since the weight of the end portion of a screwing robot is increased, it is impossible to convey a screw attracted to the driver bit from a screw supply position to a screwing position at high speed.
Prior art for magnetizing a driver bit itself has the disadvantage that the magnetic attraction of the driver bit for a screw is not strong enough to securely hold the screw. As a result, high-speed movement of a screwing robot arm from a screw supply position to a screwing position may cause the screw to drop off the driver bit and, therefore, speed-up of the screwing operation is prevented.